Intergrated semiconductor component for high-frequency measurement and use thereof

ABSTRACT

It is provided that the semiconductor component is a component of a semiconductor circuit ( 10 ) comprising a first silicon layer ( 12 ), an adjoining silicon dioxide layer (insulating layer ( 14 )) and a subsequent further silicon layer (structured layer ( 16 )) (SOI wafer), and the semiconductor component comprises an IMPATT oscillator ( 30 ), having a resonator ( 24 ) which includes a metallized cylinder ( 18 ) of silicon, disposed in the structured layer ( 16 ); a coupling disk ( 28 ) covering the cylinder ( 18 ) in the region of the first layer ( 12 ); and an IMPATT diode ( 32 ), communicating with the cylinder ( 18 ) of the resonator ( 24 ) via a recess ( 38 ) in the coupling disk ( 28 ); and a reference oscillator ( 46 ) of lower frequency, having a resonator ( 24 ) which includes a metal cylinder ( 18 ) of silicon, disposed in the structured layer ( 16 ), and coupling disk ( 28 ) covering the cylinder in the region of the first layer ( 12 ); and a microwave conductor, communicating with the cylinder ( 18 ) of the resonator ( 24 ) via a recess ( 38 ) in the coupling disk ( 28 ), and the reference oscillator, via an active oscillator circuit ( 58 ), serves the purpose of frequency stabilization of the IMPATT oscillator ( 30 ); with integrated Schottky diodes; and a transmitting and receiving antenna ( 49 ).

PRIOR ART

Semiconductor technology is increasingly being used in the automotivefield. Miniaturization not only makes improved control and regulatingtechnology for motor-specific functions possible but also opens up thepath to new safety and riding comfort systems, such as parking aids,precrash and side crash functions, blind spot detection, fill levelmeasurements, and distance measurements. For all the control—andregulation-related events, a sensor system—miniaturized as much aspossible—must be available in the motor vehicle.

As a rule, for the above fields of application named as examples,contactless sensors are used, which output a measurement beam of adefined frequency which is reflected from the object to be measured andis detected again by means of a receiver unit and evaluated.

For fill level measurements, measuring instruments in the microwaverange at about 2 to 24 GHz, which operate either on the FMCW principleor as pulse radar, are known. Such fill level sensors, for heavy-dutystationary use under problematic environmental conditions—for instancein containers with combustible substances or at high ambienttemperatures—are realized on such carrier substrates as teflon orRT-Duriod. Also known are short-range radar systems for motor vehicles,which serve as parking aids or as precrash sensors and have ameasurement frequency in the range of about 20 GHz.

For distance measurements up to ranges of 150 m, sensors employingvarious principles have been developed. Ultrasound instruments are veryeconomical, but because the beam is not sharply focused they arerelatively imprecise. Laser distance meters are substantiallymore-precise, but cannot be miniaturized arbitrarily and are veryexpensive. Distance sensors are also known with which measurements inthe microwave range can be made. The sensors required for this areindeed based on semiconductor circuits, but the requisite excitationsources (oscillators) are installed in the semiconductor circuit only byretrofitting using conventional hybrid technology. A disadvantage ofthis is that the poor replicability of the coupling of the transmissionunits to the semiconductor circuit already limits the possibleminiaturization. Moreover, the oscillators mounted retroactively on thesemiconductor circuit must be calibrated, which is complicated. Theprecision of the measurements depends, among other factors, on thestability of the transmission frequency. Reference oscillators requiredfor the frequency stabilization must then also be installed andcalibrated.

ADVANTAGES OF THE INVENTION

The integrated semiconductor component for high-frequency measurementsaccording to the invention makes it possible to realize distancemeasuring instruments that with very small dimensions makehigh-precision measurements possible. The semiconductor component isdistinguished in that it is a component of a semiconductor circuitcomprising a first silicon layer, an adjoining silicon dioxide layer(insulating layer) and a subsequent further silicon layer (structuredlayer) (SOI wafer). The semiconductor component comprises

(a) an IMPATT oscillator, having a resonator which includes a metallizedcylinder of silicon, disposed in the structured layer; a coupling diskcovering the cylinder in the region of the first layer; and an IMPATTdiode, communicating with the cylinder of the resonator via a recess inthe coupling disk; and

(b) a reference oscillator of lower frequency, having a resonator whichincludes a metal cylinder of silicon, disposed in the structured layer,and coupling disk covering the cylinder in the region of the firstlayer; and a microwave conductor, communicating with the cylinder of theresonator via a recess in the coupling disk, and the referenceoscillator, via an active oscillator circuit, serves the purpose offrequency stabilization of the IMPATT oscillator;

c) with integrated Schottky diodes; and

d) a transmitting and receiving antenna.

A system is thus created which assures measurement at very highoperating frequencies, in the millimeter wave range (120 to 130 GHz).The measurement in the microwave range makes high beam focusing possible(less than ±5° of the full width at half-maximum, so that aquasi-optical antenna serving as a receiver unit can have a lensdiameter of <30 mm. The semiconductor material used makes it possible tointegrate the required planar components by microstrip line technologyon the silicon membrane, etched open in the surroundings of thecylindrical resonators, or by coplanar technology on the surroundingsilicon base substrate. All the passive components, such asmicromechanically structured resonators, Schottky diodes and varactordiodes, as well as all the active components, such as IMPATT diodes, areintegrated on the semi-insulating SOI wafer.

In particular, it is thus advantageously achieved that no connectionwith a high-frequency signal leads downward from the system. It is thuspossible for a complete radar system to be integrated on one chip.

The IMPATT oscillator preferably generates a fixed frequency in therange from 80 to 500 GHz, in particular from 100 to 150 GHz. Thereference oscillator is preferably designed for generating a fixedfrequency in the range from 1 to 70 GHz, in particular from 20 to 50GHz. The cylinders of the resonators are each covered by an aluminumlayer approximately 1 μm thick as metallization. The coupling disks thatcover the resonators are dimensioned such that no interferingtransmission energy in the microwave range can escape from their edge.

In a preferred feature of the invention, the IMPATT oscillator isvoltage-controlled, and a varactor diode is implanted for triggeringpurposes on the edge of the coupling disk. The voltage control of theIMPATT diode is preferably effected via two low-pass filters.

The conductor layer of the semiconductor circuit serves as a carriersubstrate for a microstrip line circuit disposed over it. A patchantenna can be integrated with the semiconductor circuit. In a preferredmonostatic embodiment, the patch antenna functions as a common,circularly polarized transmitting and receiving antenna. Naturally abistatic embodiment with separate linearly or circularly polarizedtransmitting and receiving antennas is also conceivable.

Inputting the generated transmission energy of the IMPATT oscillatorinto the surrounding microstrip line circuit is done via a couplingelement. In particular, branchline couplers for decoupling fractions ofthe transmission energy into the patch antenna and for frequencystabilization with the reference oscillator may be present. The activeoscillator circuit can preferably be mounted as an additionalsemiconductor circuit on the semiconductor circuit by conventionalhybrid technology, or it can be embodied as a discrete individualtransistor. In the latter case, it is preferable for the requisiteadaptation circuit to be integrated with the semiconductor circuit bycoplanar or microstrip line technology. It is also advantageous to use afurther branchline coupler for splitting a transmission signal into anin-phase component and a quadrature component. This coupler, in the caseof a monostatic embodiment, additionally serves to separate thetransmission and reception signals.

The semiconductor components of the invention are preferably used ascomponents of a sensor for distance measurement. The sensor is intendedto be used in particular in the motor vehicle for blind spot detection,precrash and side crash detection, distance measurement, or as a parkingaid.

Further advantageous features of the invention will become apparent fromthe characteristics recited in the dependent claims.

DRAWINGS

The invention will be described in further detail below in terms ofexemplary embodiments in conjunction with the associated drawings. Shownare:

FIGS. 1 through 3, schematic sectional views through semiconductorcomponents for high-frequency applications, in various stages ofproduction;

FIG. 4, a perspective side view on a resonator for an oscillator;

FIG. 5, a schematic plan view on an IMPATT oscillator;

FIG. 6, a cross section through the semiconductor component in theregion of an IMPATT diode;

FIG. 7, a block circuit diagram of a monostatic embodiment;

FIG. 8, a block circuit diagram of a bistatic embodiment;

FIG. 9, a further illustration of a monostatic embodiment in accordancewith FIG. 7;

FIG. 10, an embodiment with a reference oscillator in an additionallymounted semiconductor circuit; and

FIG. 11, a schematic layout of a sensor for distance measurement.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1, in a schematic sectional view, shows a detail of a commerciallyavailable SOI (silicon on insulator) wafer which is used to produce asemiconductor circuit 10 with the semiconductor components of theinvention. The production, known from coplanar or planar technology, ofall the components of the semiconductor circuit 10 in one commonproduction step will not be described in further detail here—because itis well known. The wafer comprises a semi-insulating, p⁻-dopedstructured layer 16 of silicon that is 675 μm thick. It has a specificresistance in the range from 500 to 1000 Ωcm, in particular 750 Ωcm. Thestructured layer 16 is covered with an insulating layer 14 of silicondioxide, about 300 nm thick, over which a p⁻-doped layer 12 of silicon,50 μm thick, is applied.

The silicon dioxide layer 14 serves as an etching stop in trench etchingof the micromechanical structures into the structured layer 16. Thetrench etching process uncovers a membrane, comprising the precise50-μm-thick layer 12 and the 300-nm-thick layer 14, thereby creating afree space 19 in the layer 16. A silicon cylinder 18 projects into thisfree space 19 (FIG. 2) and is quasi-surrounded by the free space 19.This structuring is possible by means of suitable masking during thetrench etching.

The resultant cylindrical structure 18 is coated by vapor deposition orsputtering with an aluminum layer 20 approximately 1 μm thick (FIG. 3).The thereby metallized cylinder 18 serves as a resonator 24 of highquality (Q≈200), filled with semi-insulating silicon, which depending onthe conditions required can be excited in a targeted way in the TM₀₁₀mode or the TE₁₁₁ mode. An additional copper layer in the region of theresonator 28 that is required for heat dissipation in conventionaltechnology can be dispensed with.

A region of the layer 12 above the cylinder 18 is vapor-deposited (FIG.4) with a coupling disk 28, which extends past the cylinder 18 below it.In the coupling disk 28, a recess 38 is structured (in particular in theform of a slit). The coupling disk 28 is dimensioned such that nomicrowave energy can escape from its edge. The resonator 24 issuitable—given various dimensioning and voltage supply—as both atransmitter and a reference source. The resonator 24 for an IMPATToscillator 30 to be described in further detail below has a height ofapproximately 725 μm and a radius, adapted to the desired resonatorfrequency of 122.3 GHz, of 242 μm. For a reference frequency of 40 GHz,the radius is 800 μm for a height of 725 μm.

FIG. 5 shows a plan view on an IMPATT oscillator 30 of the kind requiredto generate a transmission signal in the microwave range. Besides theresonator 24, the IMPATT oscillator 30 includes an IMPATT diode 32,which is supplied with voltage via two low-pass filters 34, 36. TheIMPATT diode 32 is seated in the recess 38 in the coupling disk 28 andenables the connection with a microstrip line circuit integrated withthe layer 12. The transmission energy generated by the IMPATT oscillator30 is fed into the surrounding microstrip line circuit via a couplingelement 40. The IMPATT oscillator 30 can be operated in the especiallyfavorable TE₁₁₁ mode. For the case of a voltage controlled oscillator,in addition to the IMPATT diode 32, a varactor diode 42 is implanted onthe edge of the coupling disk 28 (see FIG. 9).

FIG. 6 shows a cross section through the semiconductor circuit 10 in theregion of the IMPATT diode 32. Such diodes are known, and a detaileddescription of the individual layers and function elements willtherefore be dispensed with here. Successively, the IMPATT diode 32includes an aluminum layer 33, a p⁺-doped silicon layer 35, anepisilicon layer 37, and an n⁺-doped layer 39.

The layout of a reference oscillator 46 (FIG. 9) is in principleidentical to the layout of the IMPATT oscillator 30. For operation inthe TM₀₁₀mode, however, the connection cannot be made via an IMPATTdiode 32; instead, some other suitable middle conductor must beemployed. The TM₀₁₀mode makes it possible to generate especially stablereference signals.

FIG. 7 shows a block circuit diagram of a monostatic embodiment, with acommon, circularly polarized transmitting and receiving antenna. Thearrangement includes the IMPATT oscillator 30, which generates ahigh-frequency transmission signal in the range of 122 GHz, and thereference oscillator 46, which is used for frequency stabilization andfrequency linearization. For those purposes, a fixed reference signal inthe range of 40 GHz is generated. The transmission signal is input intoa patch antenna 48 via a coupling 40. The entire semiconductor circuit10 is protected against environmental factors by a superstrate 50 in theform of a housing, shown in suggested fashion. A lens 52, which may havea diameter of less than 30 mm, focuses the emitted measurement beam. Inaddition to the monostatic embodiment shown, transmitting and receivingantennas can also be realized in the form of separate linearly orcircularly polarized units. Hence FIG. 8 shows a separate patch antenna54 and a receiver antenna 56 independent of it.

FIG. 7 shows the primary components, which are the IMPATT oscillator(transmitter) 30, frequency processor 31 and reference source (referenceoscillator 46), antenna system 49, and receiving mixer 51 withintegrated IMPATT diodes. These are integrated onto a compact chip. Nohigh-frequency connection (in the microwave range) is extended to theoutside.

Another view of the monostatic embodiment of FIG. 7, which is suitablefor radar systems for distance measurement, is shown in FIG. 9. For thefrequency stabilization, an active oscillator circuit 58 is present—inthis case in the form of an additional GaAs semiconductor circuitmounted using flip-chip technology. Alternatively, the active oscillatorcircuit 58 can be realized by a conductively glued-on discreteindividual transistor. The adaptation circuit required in that case canbe likewise integrated with the layer 12 of the semiconductor circuit 10by coplanar and microstrip line technology.

The transmission energy generated by the IMPATT oscillator 30 is used inportions, via branchline couplers 60, 62, for frequency stabilizationwith the reference oscillator 46. A further branchline coupler 64 splitsthe transmission signal into an in-phase component and a quadraturecomponent, for supplying the circularly polarized patch antenna 48, andsimultaneously accomplishes the separation of the transmission andreception signals in the monostatic system. A ratrace mixer is suppliedat one input with the reception signal from the branchline coupler 64and at its second input with the oscillator energy from the referenceoscillator 46.

FIG. 10 shows a further embodiment, in which the oscillator 46 servingas a reference is mounted as an SiGe semiconductor circuit on thesemiconductor circuit 10 by means of flip-chip bonding.

In FIG. 11, for the sake of illustration, the layout of a radar systemwith a substrate 50 and an antenna lens 52 is shown again schematically,not to scale.

1. An integrated semiconductor component for high-frequencymeasurements, characterized in that the semiconductor component is acomponent of a semiconductor circuit (10) comprising a first siliconlayer (12), an adjoining silicon dioxide layer (insulating layer (14))and a subsequent further silicon layer (structured layer (16)) (SOIwafer), and the semiconductor component comprises (a) an IMPATToscillator (30), having a resonator (24) which includes a metallizedcylinder (18) of silicon, disposed in the structured layer (16); acoupling disk (28) covering the cylinder (18) in the region of the firstlayer (12); and an IMPATT diode (32), communicating with the cylinder(18) of the resonator (24) via a recess (38) in the coupling disk (28);and (b) a reference oscillator (46) of lower frequency, having aresonator (24) which includes a metal cylinder (18) of silicon, disposedin the structured layer (16), and coupling disk (28) covering thecylinder in the region of the first layer (12); and a microwaveconductor, communicating with the cylinder (18) of the resonator (24)via a recess (38) in the coupling disk (28), and the referenceoscillator, via an active oscillator circuit (58), serves the purpose offrequency stabilization of the IMPATT oscillator (30); c) withintegrated Schottky diodes; and d) a transmitting and receiving antenna(49).
 2. The integrated semiconductor component in accordance with claim1, characterized in that the IMPATT oscillator (30) generates a fixedfrequency in the range from 80 to 500 GHz, in particular from 100 to 150GHz.
 3. The integrated semiconductor component in accordance with claim1, characterized in that the reference oscillator (46) generates a fixedfrequency in the range from 1 to 70 GHz, in particular from 30 to 50GHz.
 4. The integrated semiconductor component in accordance with claim1, characterized in that the cylinders (18) of the resonators (24) arecovered by a metal layer (20), in particular of aluminum.
 5. Theintegrated semiconductor component in accordance with claim 4,characterized in that the coupling disks (28) of the resonators (24) aredimensioned such that no transmission energy can escape from their edge.6. The integrated semiconductor component in accordance with claim 4,characterized in that the IMPATT oscillator (30) is voltage-controlled,and a varactor diode (42) is implanted on the edge of the coupling disk(28).
 7. The integrated semiconductor component in accordance with claim1, characterized in that the voltage supply to the IMPATT diode (32) iseffected via two low-pass filters (32, 34).
 8. The integratedsemiconductor component in accordance with claim 1, characterized inthat the layer (12) serves as a carrier substrate for a microstrip linecircuit.
 9. The integrated semiconductor component in accordance withclaim 1, characterized in that the semiconductor circuit (10) has apatch antenna (48) as an integrated receiver.
 10. The integratedsemiconductor component in accordance with claim 9, characterized inthat the patch antenna (48) serves as a common, circularly polarizedtransmitting and receiving antenna (monostatic embodiment).
 11. Theintegrated semiconductor component in accordance with claim 1,characterized in that the reference oscillator (46) is component of anindependent circuit mounted by hybrid technology on the semiconductorcircuit (10).
 12. The integrated semiconductor component in accordancewith claim 1, characterized in that inputting of the generatedtransmitter energy of the IMPATT oscillator (30) into the surroundingmicrostrip line circuit is effected via a coupling element (40).
 13. Theintegrated semiconductor component in accordance with claim 12,characterized in that branchline couplers (60, 62) are present fordecoupling fractions of the transmitter energy into the patch antenna(48) and for frequency stabilization with the reference oscillator (48).14. The integrated semiconductor component in accordance with claim 1,characterized in that the active oscillator circuit (58) is anadditional semiconductor circuit.
 15. The integrated semiconductorcomponent in accordance with claim 1, characterized in that the activeoscillator circuit (58) is a discrete individual transistor.
 16. Theintegrated semiconductor component in accordance with claim 15,characterized in that the requisite adaptation circuit is integrated bycoplanar or microstrip line technology into the semiconductor circuit(10).
 17. The integrated semiconductor component in accordance withclaim 1, characterized in that a further branchline coupler (64) ispresent for splitting a transmission signal into an in-phase componentand a quadrature component.
 18. The integrated semiconductor componentin accordance with claim 17, characterized in that the furtherbranchline coupler (64), in the monostatic embodiment, serves toseparate the transmission and reception signals.
 19. The use of theintegrated semiconductor component in accordance with claim 1,characterized in that the semiconductor component is a component of asensor for distance measurement.
 20. The use in accordance with claim19, characterized in that the sensor is employed in a motor vehicle forblind spot detection, precrash and side crash detection, parkingassistance, and distance measurement.